The Silk Road links east Asia and western Europe at a time when each has, in its own region, a more sophisticated commercial network than ever before.

The caravan routes of the Middle East and the shipping lanes of the Mediterranean have provided the world's oldest trading system, ferrying goods to and fro between civilizations from India to Phoenicia. Now the Roman dominance of the entire Mediterranean, and of Europe as far north as Britain, gives the merchants vast new scope to the west. At the same time a maritime link, of enormous commercial potential, opens up between India and China.

The map of the world offers no route so promising to a merchant vessel as the coastal journey from India to China. Down through the Straits of Malacca and then up through the South China Sea, there are at all times inhabited coasts not far off to either side. It is no accident that Calcutta is now at one end of the journey, Hong Kong at the other, and Singapore in the middle.

Indian merchants are trading along this route by the 1st century AD, bringing with them the two religions, Hinduism and Buddhism, which profoundly influence this entire region.

The trading kingdoms of West Africa: 5th - 15th c.

A succession of powerful kingdoms in West Africa, spanning a millennium, are unusual in that their great wealth is based on trade rather than conquest. Admittedly much warfare goes on between them, enabling the ruler of the most powerful state to demand the submission of the others. But this is only the background to the main business of controlling the caravans of merchants and camels.

These routes run north and south through the Sahara. And the most precious of the commodities moving north is African gold.

The first kingdom to establish full control over the southern end of the Saharan trade is Ghana - situated not in the modern republic of that name but in the southwest corner of what is now Mali, in the triangle formed between the Senegal river to the west and the Niger to the east.

Ghana is well placed to control the traffic in gold from Bambuk, in the valley of the Senegal. This is the first of the great fields from which the Africans derive their alluvial gold (meaning gold carried downstream in a river and deposited in silt, from which grains and nuggets can be extracted).

Like subsequent great kingdoms in this region, Ghana is at a crossroads of trade routes. The Saharan caravans link the Mediterranean markets to the north with the supply of African raw materials to the south. Meanwhile along the savannah (or open grasslands) south of the Sahara communication is easy on an east-west axis, bringing to any commercial centre the produce of the whole width of the continent.

While gold is the most valuable African commodity, slaves run it a close second. They come mainly from the region around Lake Chad, where the Zaghawa tribes make a habit of raiding their neighbours and sending them up the caravan routes to Arab purchasers in the north.

Other African products in demand around the Mediterranean are ivory, ostrich feathers and the cola nut (containing caffeine and already popular 1000 years ago as the basis for a soft drink).

The most important commodity coming south with the caravans is salt, essential in the diet of African agricultural communities. The salt mines of the Sahara (sometimes controlled by Berber tribes from the north, sometimes by Africans from the south) are as valuable as the gold fields of the African rivers (see Salt mines and caravans). Traders from the north also bring dates and a wide range of metal goods - weapons, armour, and copper either in its pure form or as brass (the alloy of copper and zinc).

These various goods, travelling some 1200 miles from one end of the trade route to the other, rarely go in a single caravan for the whole distance. They are unloaded and packed on to new transport, as specialists undertake each very different section of the journey - to the edge of the desert (either from the Mediterranean coast or from the African forest and savannah) and then from oasis to oasis through the Sahara.

In the same way goods are likely to be bought and sold on the route by specialist middlemen, with whom merchants naturally establish their own regular contacts. In this way trading partnerships develop, often made up of members of the same community or even a single family.

Vikings in Russia: from the 9th century

Unusually for the Vikings, trade rather than plunder is the main reason for their penetration deep into Russia during the 9th century AD. The rivers of eastern Europe, flowing north and south, make it surprisingly easy for goods to travel between the Baltic and the Black Sea.

One spot is particularly well-favoured as a trading centre. Near Lake Ilmen the headwaters of the Dvina, Dnieper and Volga rivers are close to each other. Respectively they flow into the Baltic, the Black Sea and the Caspian. Goods ferried by water between these important trading regions converge on this area. By the early 9th century Viking tribes known as the Rus have a base on the site of Novgorod.

Although they are not Slavs, there is justice in the Rus giving Russia her name. Their development of trade, particularly down the Dnieper (a route which becomes known as Austrvegr, or the 'Great Waterway'), lays the foundation of the Russian nation.

In 882 a Viking leader, Oleg, moves his headquarters down the Dnieper, seizing the town of Kiev. Here, in 911, he negotiates a commercial treaty with the Byzantine empire.

A Viking successor of Oleg's in Kiev, two generations later, describes how this first Russian city is the centre of a triangular trade between civilized Byzantium in the south, the steppe lands in the middle, and the wild forests of the north.

In this place 'all goods gather from all parts: gold, clothes, wine, fruits from the Greeks; silver and horses from the Czechs and Hungarians; furs, wax, honey and slaves from the Rus'.

The Pax Mongolica and the Silk Road: 13th - 14th c.

By the middle of the 13th century the family of Genghis Khan controls Asia from the coast of China to the Black Sea. Not since the days of the Han and Roman empires, when the Silk Road is first opened, has there been such an opportunity for trade. In the intervening centuries the eastern end of the Silk Road has been unsafe because of the Chinese inability to control the fierce nomads of the steppes (nomads such as the Mongols), and the western end has been unsettled by the clash between Islam and Christianity.

Now, with the Mongols policing the whole route, there is stability. In an echo of the Pax Romana, the period is often described as the Pax Mongolica.

In 1340 an Italian guide book is published giving merchants practical advice on the journey. They should let their beards grow, to be inconspicuous in Asia. They will be more comfortable if they hire a woman near the Black Sea to look after their needs on the journey. The assurance that the road is safe has an alarming ring to our ears: 'If you are some sixty men in the company, you will go as safely as if you were in your own house.' But the List of commodities changing hands on the route can be guaranteed to quicken the pulse of any ambitious trader.

Trade with the Mongol east is best known through the adventures of three Italian merchants - Marco Polo, with his father and uncle.

Hanseatic League: 12th - 17th century

In 1159 Henry the Lion, duke of Saxony and Bavaria, builds a new German town on a site which he has captured the previous year. It is Lübeck, perfectly placed to benefit from developing trade in the Baltic. Goods from the Netherlands and the Rhineland have their easiest access to the Baltic through Lübeck. For trade in the opposite direction, a short land journey from Lübeck across the base of the Danish peninsula brings goods easily to Hamburg and the North Sea.

Over the next two centuries Lübeck and Hamburg, in alliance, become the twin centres of a network of trading alliances known later as the Hanseatic League.

A Hanse is a guild of merchants. Associations of German merchants develop in the great cities on or near the Baltic (Gdansk, Riga, Novgorod, Stockholm), on the coasts of the North Sea (Bergen, Bremen) and in western cities where the Baltic trade can be profitably brokered - in particular Cologne, Bruges and London.

It suits these German merchants, and the towns which benefit from their efforts, to form mutual alliances to further the flow of trade. Safe passage for everyone's goods is essential. The control of pirates becomes a prime reason for cooperation, together with other measures (such as lighthouses and trained pilots) to improve the safety of shipping.

The rapid growth of Hanseatic trade during the 13th century is part of a general pattern of increasing European prosperity. During this period the towns with active German hanse gradually organize themselves in a more formal league, with membership fees and regular 'diets' to agree policies of mutual benefit. By the 14th century there about 100 such towns, some of them as far afield as Iceland and Spain. Their German communities effectively control the trade of the Baltic and North Sea.

But economic decline during the 14th century takes its toll on the success of the Hanseatic towns. So do political developments around the Baltic.

In 1386 Poland and Lithuania merge, soon winning the region around Gdansk from the Teutonic knights. On the opposite shore of the sea, the three Scandinavian kingdoms are united in 1389; the new monarchy encompasses Stockholm, previously an independent Hanseatic town. A century later, when Ivan III annexes Novgorod, he expels the German merchants.

Such factors contribute to the gradual decline of the Hanseatic League. What began as a positive union to promote trade becomes a restrictive league, attempting to protect German interests against foreign competitors. But great enterprises fade slowly. The final Hanseatic diet is held as late as 1669.

Ups and downs in the economy: 12th - 14th century

Throughout Europe the period from about 1150 to 1300 sees a steady increase in prosperity, linked with a rise in population. There are several reasons. More land is brought into cultivation - a process in which the Cistercians play an important part. Rich monasteries, controlled by powerful abbots, become a significant feature of feudal Europe.

In tandem with the improvement in rural wealth is the development of cities thriving on trade, in luxury goods as well as staple products such as wool.

Prominent among the trading centres of the 13th century are the coastal Italian cities, whose merchants ply the Mediterranean; Venice is particularly prosperous after the opportunities presented by the fourth crusade. In a similar way the cities of the Netherlands are well placed to profit from commerce between their three larger neighbours - England, France and the German states. And the Hanseatic towns handle the trade from the Baltic.

Together with this increase in trade goes the development of banking. Christian families, particularly in the towns of northern Italy, begin to amass fortunes by offering the financial services which have previously been the preserve of the Jews.

In the 14th century this economic prosperity falters. Land goes out of cultivation, the volume of trade drops. There are various possible reasons. There is an unusual run of disastrously bad harvests in many areas in the early part of the century. And social structures are painfully adjusting, as the old feudal system of obligations crumbles.

The final straw is the Black Death, which not only kills a third of Europe's population in 1348-9; it also ushers in an era when plague is a recurrent hazard. The 14th century is not the best in which to live. But in the 15th century - the time of the Renaissance in Europe, and the age of exploration - economic conditions improve again.

The Portuguese slave trade: 15th - 17th century

The Portuguese expeditions of the 15th century bring European ships for the first time into regular contact with sub-Saharan Africa. This region has long been the source of slaves for the route through the Sahara to the Mediterranean. The arrival of the Portuguese opens up another channel.

Nature even provides a new collection point for this human cargo. The volcanic Cape Verde Islands, with their rocky and forbidding coastlines, are uninhabited. But they contain lush tropical valleys. And they are well placed on the sea routes between West Africa, Europe and America.

Portuguese settlers move into the Cape Verde islands in about 1460. In 1466 they are given an economic advantage which guarantees their prosperity. They are granted a monopoly of a new slave trade. On the coast of Guinea the Portuguese are now setting up trading stations to buy captive Africans.

Some of these slaves are used to work the settlers' estates in the Cape Verde islands. Others are sent north for sale in Madeira, or in Portugal and Spain - where Seville now becomes an important market. Africans have been imported by this sea route into Europe since at least 1444, when one of Henry the Navigator's expeditions returns with slaves exchanged for Moorish prisoners.

The labour of the slaves in the Cape Verde Islands primes a profitable trade with the African region which becomes known as Portuguese Guinea or the Slave Coast. The slaves work in the Cape Verde plantations, growing cotton and indigo in the fertile valleys. They are also employed in weaving and dying factories, where these commodities are transformed into cloth.

The cloth is exchanged in Guinea for slaves. And the slaves are sold for cash to the slaving ships which pay regular visits to the Cape Verde Islands.

This African trade, together with the prosperity of the Cape Verde Islands, expands greatly with the development of labour-intensive plantations growing sugar, cotton and tobacco in the Caribbean and America. The Portuguese enforce a monopoly of the transport of African slaves to their own colony of Brazil. But other nations with transatlantic interests soon become the main visitors to the Slave Coast.

By the 18th century the majority of the ships carrying out this appalling commerce are British. They waste no part of their journey, having evolved the procedure known as the triangular trade.

Jacques Coeur, merchant: 1432-1451

The career of Jacques Coeur vividly suggests the opportunities open to an enterprising merchant in the 15th century. The greatest source of trading wealth is the Mediterranean, linking Christian markets in the west with Muslim ones in the east - known at this time as the Levant, the land of the rising sun.

Jacques Coeur enters this trade in 1432. He soon has seven galleys taking European cloth to the Levant and bringing back oriental spices. At Montpellier he builds a great warehouse to form the centre of his trading operation.

Agents promote Jacques Coeur's business from a string of offices which link the Mediterranean source of his wealth with the markets of western Europe. He is represented in Barcelona, Avignon, Lyons, Paris, Rouen and Bruges.

Rapid commercial success and a marked political talent soon bring Jacques Coeur influence in government. Master of the mint in Paris from 1436, he is put in charge of royal expenditure three years later. In 1441 he is ennobled. In 1442 he becomes a member of the king's council.

These are heady years in which to be close to the French court, as Charles VII recovers his kingdom in the closing stages of the Hundred Years' War. The king returns at last to Paris in 1437, the year after Jacques Coeur's appointment to head the royal mint in the capital city. When Charles wins Normandy in 1450, he is financed by a large loan from his commercial friend. Jacques Coeur enters Rouen in pomp and ceremony beside the king.

Meanwhile in Bourges, where for so many years Charles VII held his court, the merchant has built himself a house fit for a king. The Palace of Jacques Coeur, still surviving, is a spectacular example of 15th-century domestic architecture.

Such conspicuous wealth and power in an upstart brings its own dangers. Jacques Coeur has lent large sums to many in court circles. Greed and envy alike prompt his ruin. The king is persuaded that Jacques Coeur is guilty of various financial crimes and may even be responsible for the death of Charles's mistress, Agnès Sorel, in 1450.

Jacques Coeur is arrested and imprisoned in 1451. He escapes two years later and makes his way to Rome to serve the pope. All his possessions have been confiscated. Nothing survives of the mighty merchant's kingdom. Jacques Coeur's story reflects the dangers of the age - but also, even more abundantly, its opportunities.

Chinese sea trade: 15th century

The greatest extent of Chinese trade is achieved in the early 15th century when Zheng He, a Muslim eunuch, sails far and wide with a fleet of large junks. At various times between 1405 and 1433 he reaches the Persian Gulf, the coast of Africa (returning with a giraffe on board) and possibly even Australia.

Typical Chinese exports are now porcelain, lacquer, silks, items of gold and silver, and medicinal preparations. The junks return with herbs, spices, ivory, rhinoceros horn, rare varieties of wood, jewels, cotton and ingredients for making dyes.

Europe's inland waterways: 15th-17th century

Trade up and down great rivers and in coastal waters is as old as civilization. Trade across seas develops as soon as adequate boats are built, most notably by the Phoenicians. The natural next stage is to join river systems and even seas by man-made canals. Pioneered in Egypt and China in very ancient times, this development does not occur in Europe until the 15th century AD.

With prosperity beginning to pick up after the depression following the Black Death, merchants have need of cheap and reliable transport. Europe's roads are rutted tracks, the use of which is slow and dangerous. There is good commercial reason to connect the rivers, the arteries of trade. The merchants of Lübeck take the first step.

From 1391 the Stecknitz canal is constructed southwards from the city of Lübeck. Its destination is the Elbe, which is reached early in the 15th century. The new waterway joins the Baltic to the North Sea.

This canal rises some 40 feet from Lübeck to the region of Möllner and then falls the same amount again to reach the Elbe, all in a distance of 36 miles. This must be about the limit which can be safely achieved with flash locks. With mitre locks, from the 16th century, anything is possible. And the most ambitious projects are undertaken in France.

The Briare canal, completed in 1642, joins the Seine to the Loire; at one point it has a staircase of six consecutive locks to cope with a descent of 65 feet over a short distance. Even more remarkable is the Canal du Midi, completed in 1681, which joins the Mediterranean to the Atlantic by means of 150 miles of man-made waterway linking the Aude and Garonne rivers. At one point this canal descends 206 feet in 32 miles; three aqueducts are constructed to carry it over rivers; a tunnel 180 yards long pierces through one patch of high ground.

The potential of canals is self-evident. It falls to Britain, in the next century, to construct the first integrated system of waterborne traffic.